User Agent: To achieve true mobile browsing in Firefox, we need to configure the user agent. To obtain a user agent, type “Nokia E71 user agent” or whatever device you are looking for into a search engine. This generally finds the user agent you are after. For now try Nokia E71's user agent:
Mozilla/5.0 (SymbianOS/9.2; U; Series60/3.1 NokiaE71-1/110.07.127; Profile/MIDP-2.0 Configuration/CLDC-1.1 ) AppleWebKit/413 (KHTML, like Gecko) Safari/413

Now go to Tools -> Default User Agent. You will now see Nokia E71 User Agent or your device name in the list:

Click on Nokia E71 User Agent. Return to the menu and you should see it is highlighted as the user agent of choice.

You are now ready to test mobile site via Firefox.

Now visit www.getjar.com and download any App from there on pc. And:
1)After Download open that App using WordPad.
2)Locate the text ‘MIDlet-Jar-URL:’ and copy the URL next to it.
3)Paste this URL in your browser and you will get the JAR file.